Standing wave indicator for radiofrequency transmission lines



May 21,` 1946. D. w.` PETERSON 2,400,597

STANDINGv WAVE INDICATOR FOR RADIO FREQUENCY TRANSMISSION LINES Filed Oct. 6, 1943 R g www@ Fatented May 21, 1946 UNITED STAT ES PATENT OFFICE STANDING WAVE INDICATOR FOR RADIO- l IItELlIJINQYv TRANSMISSION LINES ADonalilrV. Peterson, Princeton, N. J .',k assignor to i Radio Corporation Delaware y y f Application October 6 This invention relates' to limprovements in the of America,` a corporation of art of adjusting radio frequency power networks,

and more particularly to a standing wave indicator system for radio frequency transmission` lines.

Radio frequency power transmission networks, such as are-used in radio transmitting lsystems and the like, require relatively accurate adjustment, usually at severalpoints, of the impedances presented at said points by the component transmission lines, both inv order to avoid useless disv Vsipation 4of energy and to provide proper division v of power between several load elements, for exv ample the radiators of a directive antenna. ResonantI transmission line stubs are employed as lreactive circuit elements,A particularly at ultrahigh frequencies. Such reactive elements, connectedfatl the proper points in a network, and

adjusted to lengths sothat` they present thecorrect reactances at said points, are among the means employed to secure optimum performance and efficiency of the network, in accordance with principles Well knownto those skilled in the art. It is substantially universal practice to obtain the information required `for the determination of points of connection and line lengths by means of measurements of the so-called standing'fwave ratio in a transmission line carrying energy to or from the point in the network at which the impedance is to bei adjusted.V Usually for this -purpose a special measuring line is employedA comprising a transmission line section 'constructed so that measurements' of the voltage across it at any point'may be made readily.

The measuring line is inserted in the network in series with the line on which the standing wave ratio is to be determined. The characteristic 1943, serial No. 505,252 s claims. (c1. r11-fes). l I

along its length, the voltage atleac'h'point being y noted lby the 'operator to determine the maghitude,` or ratio, and the position of the standing;v

wave. While accurate adjustment..may be attained by this method, it is extremely tedious `when applied to complexV networks, or when a large number of networks are to be adjusted.

It is the principal object of `tion to providel an improved method of, and

meansfor standing wave indication. v

Another objectY is Ato providea standing lWave indicator system providing a complete picture on gof a conventional, cathoderay'oscillof the screen n scope, thus avoiding the knecessity-for tedious and repetitive voltage measurements. f

These and other objects will become-apparent to those skilled in the art uponconsideration of the following description, with'reference to the accompanying drawing,` of which Fig. 1 isfa schematic diagram `of a standing wave indicator'system according to the invention, Fig. 2 is a longitudinal section including the probe and support structure of a folded measuring line employed iny the systernof Fig. 1, Fig. 3 is an end lView :of the structure of Fig. 2, and Fig. 4y illustrates a scale calibration for providing direct A.indication n of v standing wave ratio andV impedance angle.` .v

` t ferring to Fig. l, a radio frequency oscillator I is coupled through a coaxial transmission line 3 and a measuring line 5to a load circuit l.v By way ofexample, the oscillator I may be a radio transmitter, and the loaddevice 1 may be an antenna system. The standing wave on the' line impedance of the measuring linewill usually be y the same as that of the line to which it is connected, and the length must beat least enough so that the voltage along the line varies from its minimum to its maximum value. The ratio of the minimum value to the maximum is the standing wave ratio, and is unity when there isV no standing wave, indicating lno reflection and hence an impedance vmatch. vThe positions of voltage nodes and loops on the measuring line correspondto thoseof similar nodes and loops on the measured line, aordng indication of impedance at anyvpoint along the line and hence an indication of where stubs maybe connected.

-In prior art practice standing Wave measurements have beenmade' by means of a vacuum tube voltmeter connected to a probe which is inserted in the measuring line 'at various points 3 ViSto be indicated. k

The measuring line 5 is essentially a transmission line section, having the same characteristic impedance as the line 3, bent `into acircularcon- ,figuration YThe linel 5 is provided with a slotted outer conductor, through which a probe ,9 extends to or near the inner conductor. The probe 9 is supported on a shaft II'and coupled to a line I3 which is connected through a detector I4= to the vertical deflection circuit of a conventional cathode ray oscilloscope I5.r The shaft II is coupled to a motor I'I and carries a cam I9 for cooperation with aswitch 2|. The switch 2| is vconnected in series with a battery '.23 Vto the. synchronizing voltage input circuit of the.- oscilloscope I5.

to the cam I9, is connected between the battery 23 Aand the intensity` control circuit of the oscil--- loscope I5. The mechanical details of the'line 5 and the associated structure are described more fully hereinbel'ow.

the present inven# A second` switch 24, similar tofthe i switch 2| but angularly adjustable with respect y securedbetween a conductive disc joint 43is secured to the end "lthe operation of the above-described? system Vis as follows: rThe motor I1 rotates the cam I9 i and the probe 9, by means of cam I9 closes the switch 2l momentarily once during each revolution of the shaft II, providlng horizontal sweep synchronizing impulses for the oscilloscope I5. vAs the. probe 9 rotates, the voltage picked up by it and applied through the linel I3 to the oscilloscope I5 varies in accordance with the standing wave on the line 5. This volt-f age, amplified by the usual vertical deflection the shaft II. Thev connection to input and output linesV (notshown) such as those leading. to the oscillator I and the load 'I inrFig. v f

The invention rhas been described as a standing waveindicator for R.-F."transmission lines.

A slotted measuring line, 'bent to a circular shape,l

'..iscnnected to the lineto be measured. kA probe extends through the"'slot" in the measuringline amplifier in the oscilloscope I5,r causes the cath- Owing to'optical and screen persistence' eflects,

the line 5, v

the appearance of a continuousV curve, corre spondingto .the voltage distribution along the line 5, is presented. i l v i To facilitate measurements of standingwave v ratio and impedance angles, .a vtransparent scale,

l calibrated as shown in Fig;

y 4, may be placed over the screen-of the oscilloscope I5. Thevertical deflection gain and centering. controls are adjusted so that the cathode ray pattern fills the rvertical. scale. Since the voltage at the probe 9 becomes zero. as .the probe leavesone end of the Iline 5 to enterV l tern zero is correctly set withY respect tothe verthe other end, the deflection patticalv scale byl this adjustment. The pattern maxima are set at I, and the minimum, or maxima, occur at a vertical scale coordinate numeri ically equal to the standing wave ratio.

To read angles directly, for` determining `imfpedance the' 10aa isshort-.circuited and the hor'- izontal gain and'centering controls of the oscilloscope l5 are adjusted so that' the pattern minima occur at points `180 apart on the horizontal scale. The switch 24v is respect to the cam 2| to provide a reference mark on the deflection pattern at a point correspondingto a Voltage minimum with the load shortcircuited. With the short circuit removed,jthe.

in the vsame position and reference mark stays the angle between it and the new minimum position is indicated.

Referring to Figs. 2 and 3`the line an inner v"conductor 21 supported in'al toroidal body 29 of insulatingrmaterial such as styrene 3| and anannular conductive member 33, in grooves'of semi- 5 includes Acircular section-formed in the cooperating' surfaces of the members 3I and 33. A` circular groove 35 is cut through the members29fand 3| tothe inner conductor 21 to permit entrance of the probe 9. The probe 9 is supported in an A shortcoaxial line vsection 4I extends radially of theV disc 39 lbetween the probe 9 and a rotating joint 43. Ihe of the shaft Il by screw threads 45, and is provided at its outer end vwith coupling means 41 for engagement with complementary means on the line I3 (Fig.` l).

l The shaft II is supported on bearings 49 and 5I Vrin a conventional housingv 53.

The ends` of the lline 5 are provided with couplings 55 and 51 for ing a. secondcam operatediswitch, adjustable anmanuali;r ladjusted With gularly with respect to said shaft, and connect- Y in terms of angular and is revolved so as to sweep repeatedly throughout the length of the line. The voltage at the probe isapplied to theyvertical deflection 1; A standing ,wave `indicator. system'.k includingl said probe throughmeans including a rotatable coaxial line coupling, av 'cathode including a. vertical .deection circuit connected to said 'detector and alinear horizontal lsweep circuit, a cam operated switch on said' shaft,and l I a D.-C. source connected through said switch to.

said sweep circuit whereby said sweep circuit operatessynchronously with the rotation offsaid shaft.

.2. The invention as set forth in claim 1 includof said oscilloscope. y 3. The invention as setforth in claim 1 inuding a transparent scale lying over the screen units. 4. A* continuously direct wave indicator system including a circularmeascathode vray .os-

insulator 31 'extending through a disc 39 secured to the end of the shaft I I.

5. The invention as set forth in 6.1A continuously direct indicating lstandingr wave indicator systemfincluding. a circular 'slotthrough detector means system of a cathoderay I oscilloscope. The horizontal cathode ray rsweep probe sweep, providing ray oscilloscopeY indicating standing claim iu/,herein said cathoderay ,oscilloscope includesy a horizon- 

